Inspection Rejection: Why More Is Less in a Vision System

You rarely get anything extra for free. Engineers who work on vision systems know this. But sometimes other people believe that just putting a camera on it constitutes an effective inspection setup.

Albert Einstein has been quoted as saying, "Everything should be as simple as possible, but not simpler." I would never claim to have his level of insight -- or such an awesome head of hair -- but as an engineer, I wholeheartedly agree with this statement.

It definitely applies when it comes to computer-controlled vision systems for parts inspection. When designing a system, it can be tempting to try and include every inspection that could possibly be done. If, for instance, the machine is already being designed to check whether a bearing is missing a roller or ball, why not also inspect for the roundness of the bearing's housing or even check for surface defects? These extra steps should be simple, because the camera's already there, right?

Wrong. You rarely get anything extra for free. Engineers who work on vision systems know what I am talking about. But sometimes other people erroneously believe that just putting a camera on it constitutes an effective inspection setup.

When adding tasks for a vision system, a major challenge is lighting and camera position. Just because the light is properly set up for one inspection doesn't mean it will be correct for anything else. The result is inevitably some sort of compromise, which is never ideal. Of course, one could add a robot or other device to position all the parts for inspection, but it would add significant complexity and cost.

Another drawback of piggbacking features on to a vision system is that troubleshooting becomes harder with each additional inspection. It's incredibly frustrating to tweak a machine to pass one inspection, only to find that it often causes a malfunction elsewhere in the program.

On my first job, the inspection machinery that I oversaw was set up primarily to check for a missing pin or roller in a bearing. But it was also set up to check several other things that technically were not required or even necessary.

I was eventually able to program all these machines to look only for a missing pin -- with no loss in parts quality, interestly enough.

Later, an outside contractor was called in to update the machinery. He offered to expand its inspection capabilities. I wanted that code to remain as simple as possible. Some of these machines used a PlayStation-like controller for adjustment, so I seriously didn't want to have to do more than was absolutely necessary.

As for making things as simple as possible, but not simpler, an inspection camera shouldn't physically be more adjustable than necessary. To that end, I wish vision companies would start making holes for dowel pins standard on all their products. This feature would simplify the setup, allowing one to determine the precise camera position within a thousandth of an inch or so.

Jeremy Cook is a manufacturing engineer with 10 years of experience and has a BSME from Clemson University.

Sometimes its very important to say what features are absolutely necessary or required and what features are "Nice to have". Then a brainstorming or review can be done and that's it. Just because the tool can support and people can play with, the system should not be compexed. Many projects fail because they try to get everything on board rather than concentrating on what is required.

Adding a robot and multiple algorithms to a vision system makes it look like the AOI systems I'm used to see in PCB assembly. They are pretty expensive, being off-the-shelf. So I imagine a custom solution would be cost prohibitive.